Informing Near-Airport Satellite NO2 Retrievals Using Pandora Sky-Scanning Observations

Abstract

Airports are a large and growing source of NO_x. Tracking airport-related emissions is especially difficult, as a portion of emissions are elevated above the surface. While satellite-based NO₂ observations show hot-spots near airports, near-source retrievals often have large biases related to uncertainties in the NO₂ vertical distribution and resultant air mass factors (AMF). Here we use observations from UV–vis spectrometers (Pandora 1S, SciGlob) deployed near the Atlanta Hartsfield-Jackson International airport from April 2020–May 2021 to assess the impact of aviation on NO₂ vertical profiles. We show the first near-airport sky-scanning Pandora observations, which are used to distinguish the airport plume from the urban background. We find that increasing aviation leads to higher NO₂ over the airport, and the enhancement is distributed across the mixed layer near-equally. We compare observed profiles with those modeled by the Goddard Earth Observing System composition forecast (GEOS-CF) system. We find that modeled profiles attribute a larger portion of the column closer to the surface and underestimate the NO₂ mixing height. Observed profiles typically exhibited greater NO₂ concentrations up to 2.5 km above ground level. Air mass factors (AMF) calculated using observations (AMF_Fused) are similar over Hartsfield-Jackson to those calculated using GEOS-CF (AMF_GEOS-CF). The unexpected similarity in alternative AMFs is attributed to the altitude-dependent sensitivity of AMF_Fused to changes in NO₂ concentration. Using either AMF_Fused or AMF_GEOS-CF to evaluate TROPOMI NO₂ against independent direct-sun observations produces consistent normalized mean differences of −22% and −29%, respectively. Overall, these results demonstrate the benefits of a combined ground and satellite-based approach for probing a complex distribution of NO_x emissions in an urban area.

Observational constraints on airport-related emissions are limited. We use 3D observations from the Pandora instrument to map the near-airport NO₂ enhancement and discuss implications of discrepancies in measured and modeled NO₂ vertical profiles for interpretation of satellite-based observations.